Let me explain our second quarter results for FY 2025. This is a summary. Revenue increased by 12.5% year-over-year, thanks to the growth of existing products driven by those listed in 2024 and those subject to the Selected Treatment System, as well as the lifting of shipment limitations. Profit was significantly affected by the settlement cost of patent infringement litigation, and operating profit decreased by 27.4% year-over-year. Core operating profit was impacted by NHI drug price revisions and rising fixed expenses, including investments in human resources for future growth. It still rose 9.5% year-over-year due to increased revenue. Currently, 112 items are still subject to limited or suspended shipment. We are joining forces to strengthen our system and increase production. Although production volume was lower than planned, it has been trending upward since the second quarter.
It is now difficult to achieve the full- year production volume target. We are trying to meet the second-half target. Sales volume has continuously progressed since the first quarter. Next is an overview of the results. Revenue increased due to higher unit prices under our pricing policy and a rise in sales volume. However, operating profit decreased due to the settlement cost of the patent infringement lawsuit. The interim profit attributable to owners of the parent decreased significantly because we completed the transfer of the U.S. business and booked gains from the sales in April of last year. Revenue by product listed year. Sales of existing products are increasing thanks to the Selected Treatment System's impact. We are now aiming to gain market share with new products to be launched in December 2025. This is an analysis of the change in core operating profit.
Despite being impacted by a lower NHI drug price and increased fixed costs such as labor and depreciation, gross profit increased year-over-year as revenue grew. Core operating profit increased by around JPY 1.2 billion year-over-year. This page discusses the change in total operating profit. The difference between total and core operating profits was the inclusion of patent lawsuit settlement costs in total operating income. This page explains the reasons for the gaps between the first half results and our initial plan. As for cost of goods sold, strong sales and a rise in the cost ratio due to a decline in production volume were the reasons. Overall, the lower than expected gross profit was almost offset by the lower SG&A. However, due to the settlement cost, the operating profit does not meet our initial plan. Finally, we have revised our full- year guidance for FY 2025.
Based on the results in the first half of the year, we revised our full year forecast. Regarding the guidance for the second half of the year, we are maintaining the original numbers. You can find reference information about financial data and more on pages nine and beyond. This concludes my explanation of our second quarter results for fiscal year 2025.